The present process relates to the manufacture of electrochemical fuel cells. More specifically, the present invention provides a double belt process and apparatus for bonding electrochemical fuel cell MEA materials comprising an ion exchange membrane material and at least one electrode substrate.
Electrochemical fuel cells convert reactants, namely, fuel and oxidant fluid streams, to generate electric power and reaction products. Electrochemical fuel cells employ an electrolyte disposed between two electrodes, namely a cathode and an anode. The electrodes generally each comprise a porous, electrically conductive sheet material and an electrocatalyst disposed at the interface between the electrolyte and the electrode layers to induce the desired electrochemical reactions. The location of the electrocatalyst generally defines the electrochemically active area.
Solid polymer fuel cells typically employ a membrane electrode assembly (xe2x80x9cMEAxe2x80x9d) consisting of a solid polymer electrolyte or ion exchange membrane disposed between two electrode layers. The membrane, in addition to being ion conductive (typically proton conductive) material, also acts as a barrier for isolating the reactant streams from each other.
The advantagesxe2x80x94both actual and potentialxe2x80x94of electrochemical fuel cells are well documented. Until recently, however, high-volume fuel cell manufacturing processes have been relatively tangential concerns. The primary focus for fuel cell manufacturers has been (and, in many respects, will continue to be) to design and develop efficient fuel cells of consistent and high quality. Now, in addition to further research and development of fuel cells and their applications, manufacturers are focusing more attention on developing high-volume, commercial manufacturing processes.
Conventional methods for producing MEAs include reciprocal press bonding and roller bonding. Such methods are not particularly well suited to high-volume manufacturing processes, may not allow for a suitable degree of control over the bonding temperatures or pressures employed, or both.
In a process for the manufacture of an MEA for an electrochemical cell, an ion-exchange membrane material is bonded to at least one electrode substrate. In one embodiment, the present process comprises: feeding a sheet of ion exchange membrane material through a double belt press; feeding at least one electrode substrate through the double belt press; and applying heat and pressure to bond a portion of the membrane material and the electrode substrate(s) within a process zone of the double belt press. The present process can further comprise cutting the bonded MEA material to size.
In another embodiment, the present process further comprises receiving bonded material from the double belt press and longitudinal cutting of the bonded material to obtain at least one strip of bonded material. For example, the cutting steps can comprise longitudinal cutting to the desired width with a spring-loaded knife.
In another embodiment, the present process further comprises receiving bonded material from the double belt press and cross-cutting the bonded material. For example, mechanical cross-cutting to a desired length with a guillotine cutter can be employed.
In the foregoing embodiments, the process can further comprise a punching step wherein features such as manifold openings or rounded corners can be added to the MEA material. A variety of cutting processes can be employed in the present method to cut the bonded material to size, if desired, including mechanical cutting, laser cutting, high pressure water jet cutting and ultrasonic cutting.
The present double belt bonding process specifically contemplates bonding a continuous ion exchange membrane material sheet with one or two continuous electrode substrate sheets. The present process also contemplates feeding of discrete ion exchange membrane material sheets and/or electrode substrate sheets. Further, the process can also involve depositing, such as by extruding, sputtering or spraying, for example, one or more of the MEA components in powder, granulate, paste or liquid form onto at least one of the steel belts of a double belt press, and then forming the component layer(s) and bonding the MEA. Alternatively, at least one of the components can be deposited onto a sheet of another of the MEA components to be fed through the double belt press.
In one embodiment, the present apparatus comprises a double belt press and means for depositing a powder, granulate, paste or liquid MEA component mixture onto a material or onto one of the belts of the double belt press, wherein the material includes ion exchange membrane materials, electrode substrates and release films.